An inverter is an electrical device enabling generation of a voltage with a variable frequency. One example of an inverter is a converter bridge implemented by IGB transistors (IGBT, Insulated-gate Bipolar Transistor) or other power semiconductors. Inverters may be used in connection with motors for driving them with a variable frequency. An inverter may also be a part of a frequency converter used for driving a motor or another load, for example. A frequency converter can include two converters (i.e., a rectifier and an inverter), between which there is a direct-voltage or direct-current intermediate circuit. The rectifier and the inverter may also be positioned physically apart from each other, and one rectifier may feed several inverters via a common intermediate circuit or, alternatively, several rectifiers may feed one inverter. An example of a rectifier is a diode bridge or a thyristor bridge.
FIG. 1 shows an example of an electric drive having a frequency converter 40 and an electric motor 20 such as an asynchronous motor or a synchronous motor. The exemplary frequency converter 40 is composed of two converters, a rectifier 30 and an inverter 10, between which is provided a direct voltage intermediate circuit 50. The rectifier 30 obtains its supply from an alternating current (AC) source, which is for instance a 50- or 60-Hz alternating current network. As illustrated in the example of FIG. 1, the supply from the output of the inverter 10 to the motor 20 may be a three-phase alternating current connection, for example.
The efficiency of an electric drive can depend on several variables such as an output voltage of the inverter or a flux of the motor and a switching frequency of the inverter. Moreover, the operating point in which the electric drive is running can also effect optimal values of these variables. As a result, the operating parameters of the inverter of the electric drive should be accommodated to the properties of the motor of the electric drive such that the electric drive can be operated as efficiently as possible. This could be done by numerical computing using known motor parameters.
However, the motor parameters may not always be known accurately enough in order to determine optimal operating parameters for the electric drive.